All Hands On Deck

Sun Herald

Sunday October 14, 2007

with Scott McGregor

Get into the spirit of summer with a deck that any DIYer can tackle.

YOU MAY be an experienced DIYer or a novice ready to move beyond the basics, either way building your own deck is a great project to take on over a weekend or two. No two decks are the same. Some rely on standard design and construction techniques while others are complex multi-level structures spanning many square metres and encompassing water features, stairways or protruding trees. The basic one I built for a friend recently is a fairly typical example, offering extended floor space on which to enjoy a morning coffee in the sun and an elevated vantage point to keep an eye on the kids as they play in the garden below.

Planning

A new deck should start with a scale diagram. Lay some lengths of timber out on the ground to get a feel for the size and shape required and then transcribe those dimensions to a diagram laid out on some graph paper or to simple drawing software. Remember to check with your council. Many decks do not require council permission as long as they fall within a few simple guidelines. Remember that if the surface of your deck is any higher than one metre from the ground, handrails will be required.

Construction

A deck is like a floor; it has joists to support the flooring material (decking) and posts and bearers to hold the joists up off the ground. The dimensions and quantities of each of the framing elements are determined by the design of the frame and the distances they should span. To help determine these, consult a span table - span tables are laid out by engineers and are based on the load capacities of various timber species and sizes and they're available from timber merchants; ask the timber merchants to assist you in selecting the correct timbers for your deck.

For this simple deck, three H4 treated pine poles were chosen as posts to support the front edge, each 2.4 metres apart and imbedded at least 600 millimetres into the ground. The posts extend above the surface of the deck so they can double as balustrade supports.

The H numbers on timber indicate its durability and resistance to rot and vermin. The building code requires a durability rating of H4 or higher for timber that comes into contact with the ground. Once positioned, each of the posts was held in place with diagonal timber braces while the concrete footing was poured. Most of these temporary braces can stay in place until the rest of the deck is constructed.

The back edge of the deck is supported by the house. Joists are supported by a timber plate or ledger bolted to the sub-floor frame. The front of the joists are, in turn, supported on a timber bearer that is bolted to the posts. Each post has a rebate cut into it to house this bearer and a 10-millimetre-thick galvanised bolt fastened through to keep everything locked together. The top surface of the ledger and the bearer are level with each other. This level position was determined with an inexpensive laser tool, although you can use a spirit level.

The joists were then positioned 450 millimetres from centre to centre. This spacing is an important aspect of the structural design as it has a direct bearing on the size and type of timber used. When selecting timber for bearers and joists, H numbers are quoted in the span tables. The higher the H number, the stronger the timber and greater its ability to span distances and support weight. Each joist, once positioned, is affixed to the bearer with a pair of nails skewed in through its sides.

Surface choices

What timber should your deck surface be? Hardwood and treated pine are the common choices and each has its pros and cons.

Treated pine decking is now preserved with non-arsenic based treatments so you can feel confident about leaving it unfinished . It is produced in fast-growing plantations, is inexpensive and easy to use.

Hardwood decking is a better choice if you live in an area designated as a fire zone. Although it is a little more expensive and tougher to work with, it is, in my opinion, more attractive. It looks terrific left in its natural state and allowed to silver off or treated with natural decking oil to highlight the range of red and brown colours.

Tips

Lay all your decking boards out first to mix and match colours, alternate joins and separate badly warped boards before you start. When nailing hardwood decking into hardwood framing it is very important to pre-drill your nail holes to prevent timber splitting and nails bending, it also helps to rub each nail on a cake of soap or some wax to help smooth its way into the timber. To obtain a neat finish at the edge of a deck, lay all the boards with the ends overhanging the frame and then, once they are affixed, mark a straight line across the overhang and then use a circular saw to trim them all off at once.

© 2007 Sun Herald

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